Name
EXT_packed_depth_stencil
Name Strings
GL_EXT_packed_depth_stencil
Contributors
Pat Brown
Matt Craighead
Cass Everitt
Michael Gold
Evan Hart
Jeff Juliano
John Kessenich
Mark Kilgard
Jon Leech
Bill Licea-Kane
Barthold Lichtenbelt
Kent Lin
Brian Paul
Ian Romanick
John Rosasco
Jeremy Sandmel
Contact
Jeff Juliano, NVIDIA Corporation (jjuliano 'at' nvidia.com)
Status
Incomplete
Version
Last Modified Date: September 26, 2005
Revision: #12
Number
312
Dependencies
OpenGL 1.1 and EXT_framebuffer_object are required.
Written based on the wording of the OpenGL 2.0 specification.
Written based on the wording of EXT_framebuffer_object version 117.
This extension interacts with EXT_framebuffer_object.
This extension modifies NV_packed_depth_stencil.
ARB_depth_texture affects the definition of this extension.
SGIX_depth_texture affects the definition of this extension.
Overview
Many OpenGL implementations have chosen to interleave the depth and
stencil buffers into one buffer, often with 24 bits of depth
precision and 8 bits of stencil data. 32 bits is more than is
needed for the depth buffer much of the time; a 24-bit depth buffer,
on the other hand, requires that reads and writes of depth data be
unaligned with respect to power-of-two boundaries. On the other
hand, 8 bits of stencil data is more than sufficient for most
applications, so it is only natural to pack the two buffers into a
single buffer with both depth and stencil data. OpenGL never
provides direct access to the buffers, so the OpenGL implementation
can provide an interface to applications where it appears the one
merged buffer is composed of two logical buffers.
One disadvantage of this scheme is that OpenGL lacks any means by
which this packed data can be handled efficiently. For example,
when an application reads from the 24-bit depth buffer, using the
type GL_UNSIGNED_SHORT will lose 8 bits of data, while
GL_UNSIGNED_INT has 8 too many. Both require expensive format
conversion operations. A 24-bit format would be no more suitable,
because it would also suffer from the unaligned memory accesses that
made the standalone 24-bit depth buffer an unattractive proposition
in the first place.
Many applications, such as parallel rendering applications, may also
wish to draw to or read back from both the depth and stencil buffers
at the same time. Currently this requires two separate operations,
reducing performance. Since the buffers are interleaved, drawing to
or reading from both should be no more expensive than using just
one; in some cases, it may even be cheaper.
This extension provides a new data format, GL_DEPTH_STENCIL_EXT,
that can be used with the glDrawPixels, glReadPixels, and
glCopyPixels commands, as well as a packed data type,
GL_UNSIGNED_INT_24_8_EXT, that is meant to be used with
GL_DEPTH_STENCIL_EXT. No other data types are supported with
GL_DEPTH_STENCIL_EXT. If ARB_depth_texture or SGIX_depth_texture is
supported, GL_DEPTH_STENCIL_EXT/GL_UNSIGNED_INT_24_8_EXT data can
also be used for textures; this provides a more efficient way to
supply data for a 24-bit depth texture.
GL_DEPTH_STENCIL_EXT data, when passed through the pixel path,
undergoes both depth and stencil operations. The depth data is
scaled and biased by the current GL_DEPTH_SCALE and GL_DEPTH_BIAS,
while the stencil data is shifted and offset by the current
GL_INDEX_SHIFT and GL_INDEX_OFFSET. The stencil data is also put
through the stencil-to-stencil pixel map.
glDrawPixels of GL_DEPTH_STENCIL_EXT data operates similarly to that
of GL_STENCIL_INDEX data, bypassing the OpenGL fragment pipeline
entirely, unlike the treatment of GL_DEPTH_COMPONENT data. The
stencil and depth masks are applied, as are the pixel ownership and
scissor tests, but all other operations are skipped.
glReadPixels of GL_DEPTH_STENCIL_EXT data reads back a rectangle
from both the depth and stencil buffers.
glCopyPixels of GL_DEPTH_STENCIL_EXT data copies a rectangle from
both the depth and stencil buffers. Like glDrawPixels, it applies
both the stencil and depth masks but skips the remainder of the
OpenGL fragment pipeline.
glTex[Sub]Image[1,2,3]D of GL_DEPTH_STENCIL_EXT data loads depth and
stencil data into a depth_stencil texture. glGetTexImage of
GL_DEPTH_STENCIL_EXT data can be used to retrieve depth and stencil
data from a depth/stencil texture.
In addition, a new base internal format, GL_DEPTH_STENCIL_EXT, can
be used by both texture images and renderbuffer storage. When an
image with a DEPTH_STENCIL_EXT internal format is attached to both
the depth and stencil attachment points of a framebuffer object (see
EXT_framebuffer_object), then it becomes both the depth and stencil
buffers of the framebuffer. This fits nicely with hardware that
interleaves both depth and stencil data into a single buffer. When
a texture with DEPTH_STENCIL_EXT data is bound for texturing, only
the depth component is accessible through the texture fetcher. The
stencil data can be written with TexImage or CopyTexImage, and can
be read with GetTexImage. When a DEPTH_STENCIL_EXT image is
attached to the stencil attachment of the bound framebuffer object,
the stencil data can be accessed through any operation that reads
from or writes to the framebuffer's stencil buffer.
New Procedures and Functions
None.
New Tokens
Accepted by the parameter of DrawPixels, ReadPixels,
TexImage1D, TexImage2D, TexImage3D, TexSubImage1D, TexSubImage2D,
TexSubImage3D, and GetTexImage, by the parameter of
CopyPixels, by the parameter of TexImage1D,
TexImage2D, TexImage3D, CopyTexImage1D, CopyTexImage2D, and
RenderbufferStorageEXT, and returned in the parameter of
GetTexLevelParameter and GetRenderbufferParameterivEXT:
DEPTH_STENCIL_EXT 0x84F9
Accepted by the parameter of DrawPixels, ReadPixels,
TexImage1D, TexImage2D, TexImage3D, TexSubImage1D, TexSubImage2D,
TexSubImage3D, and GetTexImage:
UNSIGNED_INT_24_8_EXT 0x84FA
Accepted by the parameter of TexImage1D,
TexImage2D, TexImage3D, CopyTexImage1D, CopyTexImage2D, and
RenderbufferStorageEXT, and returned in the parameter of
GetTexLevelParameter and GetRenderbufferParameterivEXT:
DEPTH24_STENCIL8_EXT 0x88F0
Accepted by the parameter of GetTexLevelParameter:
TEXTURE_STENCIL_SIZE_EXT 0x88F1
Additions to Chapter 2 of the OpenGL 2.0 Specification (OpenGL
Operation)
Starting with the bullet list on page 86, update section 2.15.4
"Shader Execution" to say:
"* The sampler used in a texture lookup function is of type
sampler1D or sampler2D, and the texture object's base internal
format is DEPTH_COMPONENT or DEPTH_STENCIL_EXT, and the
TEXTURE_COMPARE_MODE is not NONE.
* The sampler used in a texture lookup function is of type
sampler1DShadow or sampler2DShadow, and the texture object's base
internal format is DEPTH_COMPONENT or DEPTH_STENCIL_EXT, and the
TEXTURE_COMPARE_MODE is NONE.
* The sampler used in a texture lookup function is of type
sampler1DShadow or sampler2DShadow, and the texture object's base
internal format is not DEPTH_COMPONENT or DEPTH_STENCIL_EXT.
The stencil index texture internal component is ignored if the base
internal format is DEPTH_STENCIL_EXT.
If a vertex shader uses..."
Additions to Chapter 3 of the OpenGL 2.0 Specification (Rasterization)
Update the first paragraph on page 118, in the definition of
ColorTable, to say:
"... The COLOR_INDEX, DEPTH_COMPONENT, DEPTH_STENCIL_EXT,
and STENCIL_INDEX and the BITMAP are not allowed."
Update the third paragraph on page 118, in the definition of
ColorTable, to say:
"... must be one of the formats in table 3.15 or
table 3.16, other than the DEPTH or DEPTH_STENCIL_EXT formats in
those tables."
On page 121, update the first paragraph in the definition of
ConvolutionFilter2D to say:
"... The formats COLOR_INDEX, DEPTH_COMPONENT, DEPTH_STENCIL_EXT,
and STENCIL_INDEX and the type BITMAP are not allowed."
Update the paragraph that spans pages 121 and 122, in the definition
of ConvolutionFilter2D, to say:
"... must be one of the formats in table 3.15 or
table 3.16, other than the DEPTH or DEPTH_STENCIL_EXT formats in
those tables."
Update the third paragraph on page 125, in the definition of
Histogram, to say:
"... The error INVALID ENUM is generated if internalformat is not
one of the formats in table 3.15 or table 3.16, or is 1, 2, 3, 4, or
any of the DEPTH_COMPONENT or DEPTH_STENCIL_EXT or INTENSITY formats
in those tables."
On page 126, update the second paragraph in the definition of Minmax
to say:
"... The error INVALID ENUM is generated if internalformat is not
one of the formats in table 3.15 or table 3.16, or is 1, 2, 3, 4, or
any of the DEPTH_COMPONENT or DEPTH_STENCIL_EXT or INTENSITY formats
in those tables. The resulting..."
Add a row to Table 3.5 (page 128):
type Parameter GL Type Special
------------------------------------------------
... ... ...
UNSIGNED_INT_2_10_10_10_REV uint Yes
UNSIGNED_INT_24_8_EXT uint Yes
Update the paragraph on page 128, in the definition of DrawPixels,
to say:
"... If the GL is in color index mode and is not one of
COLOR_INDEX, STENCIL_INDEX, DEPTH_COMPONENT, or DEPTH_STENCIL_EXT,
then the error INVALID_OPERATION occurs. If is BITMAP and
is not COLOR_INDEX or STENCIL_INDEX then the error
INVALID_ENUM occurs. If is DEPTH_STENCIL_EXT and is
not UNSIGNED_INT_24_8_EXT then the error INVALID_ENUM occurs. Some
additional constraints on the combinations of and
values that are accepted is discussed below."
Add a row to Table 3.6 (page 129):
Format Name Element Meaning and Order Target Buffer
------------------------------------------------------------------
... ... ...
DEPTH_COMPONENT Depth Depth
DEPTH_STENCIL_EXT Depth and Stencil Index Depth and Stencil
... ... ...
Add a row to Table 3.8 (page 132):
type Parameter GL Type Components Pixel Formats
------------------------------------------------------------------
... ... ... ...
UNSIGNED_INT_2_10_10_10_REV uint 4 RGBA,BGRA
UNSIGNED_INT_24_8_EXT uint 2 DEPTH_STENCIL_EXT
Update the last paragraph on page 130 to say:
"Calling DrawPixels with a of UNSIGNED_BYTE_3_3_2, ...,
UNSIGNED_INT_2_10_10_10_REV, or UNSIGNED_INT_24_8_EXT is a special
case in which all the components of each group are packed into a
single unsigned byte, unsigned short, or unsigned int, depending on
the type."
Add the following diagram to Table 3.11 (page 134):
UNSIGNED_INT_24_8_EXT
31 30 29 28 27 26 ... 12 11 10 9 8 7 6 5 4 3 2 1 0
+----------------------------------+---------------+
| 1st Component | 2nd Component |
+----------------------------------+---------------+
Add a row to Table 3.12 (page 135):
Format | 1st 2nd 3rd 4th
------------------+-------------------------------
... | ... ... ... ...
BGRA | blue green red alpha
DEPTH_STENCIL_EXT | depth stencil N/A N/A
Add the following paragraph to the end of the section "Conversion to
floating-point" (page 135-136):
"For groups of components that contain both standard components and
index elements, such as DEPTH_STENCIL_EXT, the index elements are
not converted."
Update the last paragraph in the section "Conversion to Fragments"
(page 137) to say:
"... Groups arising from DrawPixels with a of STENCIL_INDEX
or DEPTH_STENCIL_EXT are treated specially and are described in
section 4.3.1."
Update the first paragraph of section 3.6.5 "Pixel Transfer
Operations" (pages 137-138) to say:
"The GL defines five kinds of pixel groups:
1. RGBA component: Each group comprises four color components:
red, green, blue, and alpha.
2. Depth component: Each group comprises a single depth
component.
3. Color index: Each group comprises a single color index.
4. Stencil index: Each group comprises a single stencil index.
5. Depth/stencil: Each group comprises a single depth component
and a single stencil index."
Update the first paragraph in the section "Arithmetic on Components"
(page 138) to say:
"This step applies only to RGBA component and depth component
groups, and to the depth components in depth/stencil groups. ..."
Update the first paragraph in the section "Arithmetic on Indices"
(page 138) to say:
"This step applies only to color index and stencil index groups, and
to the stencil indices in depth/stencil groups. ..."
Update the first paragraph in the section "Stencil Index Lookup"
(page 139) to say:
"This step applies only to stencil index groups and to the stencil
indices in depth/stencil groups. ..."
In section 3.8.1 "Texture Image Specification", update page 151 to
say:
"The selected groups are processed exactly as for DrawPixels,
stopping just before final conversion. Each R, G, B, A, or depth
value so generated is clamped to [0, 1], while the stencil index
values are masked by 2^n-1, where n is the number of stencil bits in
the internal format resolution (see below). If the base internal
format is DEPTH_STENCIL_EXT and is not DEPTH_STENCIL_EXT,
then the values of the stencil index texture component are
undefined.
Components are then selected from the resulting R, G, B, A, depth,
or stencil index values to obtain a texture with the base internal
format specified by (or derived from) . Table 3.15
summarizes the mapping of R, G, B, A, depth, or stencil values to
texture components, as a function of the base internal format of the
texture image. may be specified as one of the
eight internal format symbolic constants listed in table 3.15, as
one of ...
Textures with a base internal format of DEPTH_COMPONENT or
DEPTH_STENCIL_EXT are supported by texture image specification
commands only if is TEXTURE_1D, TEXTURE_2D,
PROXY_TEXTURE_1D or PROXY_TEXTURE_2D. Using this format in
conjunction with any other will result in an
INVALID_OPERATION error.
Textures with a base internal format of DEPTH_COMPONENT or
DEPTH_STENCIL_EXT require either depth component data or
depth/stencil component data. Textures with other base internal
formats require RGBA component data. The error INVALID_OPERATION is
generated if the base internal format is DEPTH_COMPONENT or
DEPTH_STENCIL_EXT and is not DEPTH_COMPONENT or
DEPTH_STENCIL_EXT, or if the base internal format is not
DEPTH_COMPONENT or DEPTH_STENCIL_EXT and is DEPTH_COMPONENT
or DEPTH_STENCIL_EXT."
Update the second paragraph on page 152 to say:
"...the mapping of the R, G, B, A, depth and stencil values to
texture components..."
Update the third paragraph on page 152 to say:
"...the mapping of the R, G, B, A, depth, and stencil values to
texture components..."
Add a row to table 3.15 (page 153), and update the title of the
second column:
Base Internal Format RGBA and Depth and Stencil Values Internal Components
----------------------------------------------------------------------------
... ... ...
DEPTH_STENCIL_EXT Depth,Stencil D,S
... ... ...
Update the caption for table 3.15 (page 153)
"Table 3.15: Conversion from RGBA, depth, and stencil pixel
components to internal texture, table, or filter components. See
section 3.8.13 for a description of the texture components R, G, B,
A, L, I, D, and S."
Add a new column to table 3.16 (page 153) labled "S bits". The
value of this column is blank for all rows except a new row:
Sized Base R G B A L I D S
Internal Format InternalFormat bits bits bits bits bits bits bits bits
------------------------------------------------------------------------------
... ... ... ... ... ... ... ... ... ...
DEPTH24_STENCIL8_EXT DEPTH_STENCIL_EXT 24 8
... ... ... ... ... ... ... ... ... ...
Update the second paragraph on page 159, in the definition of
CopyTexImage2D, to say:
"...The image is taken from the framebuffer exactly as if these
arguments were passed to CopyPixels with argument type set to COLOR
DEPTH, or DEPTH_STENCIL_EXT, depending on , stopping
after pixel transfer processing is complete. RGBA data is taken
from the current color buffer, while depth component and stencil
index data are taken from the depth and stencil buffers,
respectively. If depth component data is required and no depth
buffer is present, or if stencil index data is required and there is
no stencil buffer, the error INVALID_OPERATION is generated.
Subsequent processing is identical to that described for TexImage2D,
beginning with clamping of the R, G, B, A, or depth values, and
masking of the stencil index value, from the resulting pixel
groups..."
Update the third paragraph on page 161 to say:
"...except that the assignment of R, G, B, A, depth, and stencil
pixel group values to the texture components is controlled by the
internalformat of the texture array, not by an argument to the
command..."
Update section 3.8.5 "Depth Component Textures" (page 168) to say:
"Depth textures and the depth components of depth/stencil textures
can be treated as LUMINANCE, INTENSITY or ALPHA textures during
texture filtering and application. The initial state for depth and
depth/stencil textures treats them as LUMINANCE textures."
Add a new section between sections 3.8.9 and 3.8.10, after the first
paragraph on page 177:
"3.8.9-1/2 DEPTH/STENCIL Textures
If the texture image has a base internal format of
DEPTH_STENCIL_EXT, then the stencil index texture component is
ignored. The texture value Tau does not include a stencil index
component, but includes only the depth component."
Update the first paragraph of section 3.8.11 "Texture State and
Proxy State" on page 178 to say:
"...eight integer values describing the resolutions of each of the
red, green, blue, alpha, luminance, intensity, depth, and stencil
components of the image..."
Update the second paragraph on page 179 to say:
"... and internal format state values, as well as state for the red,
green, blue, alpha, luminance, intensity, depth, and stencil
component resolutions."
Update the first paragraph of "Depth Texture Comparison Mode" in
section 3.8.14 on page 188 to say:
"If the currently bound texture's base internal format is
DEPTH_COMPONENT or DEPTH_STENCIL_EXT..."
Update the first paragraph of section 3.8.15 "Texture Application",
on page 189, to say:
"...Otherwise, a texture value is found according to the parameter
values of the currently bound texture image of the appropriate
dimensionality using the rules given in sections 3.8.6 through
3.8.9. Note that the texture value may contain R, G, B, A, L, I, or
D components, but it does not contain an S component. If the
texture's base internal format is DEPTH_STENCIL_EXT, for the
purposes of texture application, it is as if the base internal
format was DEPTH..."
Starting with the bullet list on page 195, update section 3.11.2
"Shader Execution" to say:
"* The sampler used in a texture lookup function is of type
sampler1D or sampler2D, and the texture object's base internal
format is DEPTH_COMPONENT or DEPTH_STENCIL_EXT, and the
TEXTURE_COMPARE_MODE is not NONE.
* The sampler used in a texture lookup function is of type
sampler1DShadow or sampler2DShadow, and the texture object's base
internal format is DEPTH_COMPONENT or DEPTH_STENCIL_EXT, and the
TEXTURE_COMPARE_MODE is NONE.
* The sampler used in a texture lookup function is of type
sampler1DShadow or sampler2DShadow, and the texture object's base
internal format is not DEPTH_COMPONENT or DEPTH_STENCIL_EXT.
The stencil index texture internal component is ignored if the base
internal format is DEPTH_STENCIL_EXT.
If a fragment shader uses..."
Additions to Chapter 4 of the OpenGL 2.0 Specification (Per-Fragment
Operations and the Frame Buffer)
Replace section 4.3.1 "Writing to the Stencil Buffer" (page 218)
with the following:
"4.3.1 Writing to the Stencil Buffer or to the Depth and Stencil
Buffers
The operation of DrawPixels was described in section 3.6.4, except
if the argument was STENCIL_INDEX or DEPTH_STENCIL_EXT. In
this case, all operations described for DrawPixels take place, but
window (x,y) coordinates, each with the corresponding stencil index,
or depth value and stencil index, are produced in lieu of fragments.
Each coordinate-data pair is sent directly to the per-fragment
operations, bypassing the texture, fog, and antialiasing application
stages of rasterization. Each pair is then treated as a fragment
for purposes of the pixel ownership and scissor tests; all other
per-fragment operations are bypassed. Finally, each stencil index
is written to its indicated location in the framebuffer, subject to
the current front stencil mask (set with StencilMask or
StencilMaskSeparate). If a depth component is present, and if the
setting of DepthMask is not FALSE, the depth component is also
written to the framebuffer; the setting of DepthTest is ignored.
The error INVALID_OPERATION results if the argument is
STENCIL_INDEX and there is no stencil buffer, or if is
DEPTH_STENCIL_EXT and there is neither a depth nor a stencil
buffer."
Add the following paragraph after the second paragraph of the
section "Obtaining Pixels from the Framebuffer" (page 219):
"If the is DEPTH_STENCIL_EXT, then values are taken from
both the depth buffer and the stencil buffer. If there is no depth
buffer or if there is no stencil buffer, then the error
INVALID_OPERATION occurs. If the parameter is not
UNSIGNED_INT_24_8_EXT, then the error INVALID_ENUM occurs.
If there is a multisample buffer, then values are obtained from the
depth and stencil samples in this buffer. It is recommended that the
depth and stencil values of the centermost sample be used, though
implementations may choose any function of the depth and stencil
sample values at each pixel."
Update the third paragraph on page 221 to say:
"... If the GL is in color index mode, and is not
DEPTH_COMPONENT, STENCIL_INDEX, or DEPTH_STENCIL_EXT, then the color
index is obtained at each pixel location."
Update the first sentence of the section "Conversion of RGBA values"
(page 222) to say:
"This step applies only if the GL is in RGBA mode, and then only if
is neither STENCIL_INDEX, DEPTH_COMPONENT, nor
DEPTH_STENCIL_EXT."
Update the section "Conversion of Depth values" (page 222) to say:
"This step applies only if is DEPTH_COMPONENT or
DEPTH_STENCIL_EXT. Each element taken from the depth buffer is
taken to be a fixed-point value in [0,1] with m bits, where m is the
number of bits in the depth buffer (see section 2.11.1)."
Add a row to Table 4.6 (page 223):
type Parameter Index Mask
---------------------------------
... ...
INT 2^31-1
UNSIGNED_INT_24_8_EXT 2^8-1
Update the second and third paragraphs of section 4.3.3 (page 223)
to say:
" is a symbolic constant that must be one of COLOR, STENCIL,
DEPTH, or DEPTH_STENCIL_EXT, indicating that the values to be
transferred are colors, stencil values, depth values, or
depth/stencil pairs, respectively. The first four arguments have the
same interpretation as the corresponding arguments to ReadPixels.
Values are obtained from the framebuffer, converted (if
appropriate), then subjected to the pixel transfer operations
described in section 3.6.5, just as if ReadPixels were called with
the corresponding arguments. If the is STENCIL or DEPTH,
then it is as if the for ReadPixels were STENCIL_INDEX, or
DEPTH_COMPONENT, respectively. If the is DEPTH_STENCIL_EXT,
then it is as if the for ReadPixels were specified as
described in table 4.6b. If the is COLOR, then if the GL is
in RGBA mode, it is as if the were RGBA, while if the GL is
in color index mode, it is as if the were COLOR_INDEX."
Add Table 4.6b:
DEPTH_BITS STENCIL_BITS format
-------------------------------------------
zero zero DEPTH_STENCIL_EXT
zero non-zero DEPTH_COMPONENT
non-zero zero STENCIL_INDEX
non-zero non-zero DEPTH_STENCIL_EXT
Table 4.6b: Effective ReadPixels format for DEPTH_STENCIL_EXT
CopyPixels operation.
Add a row to Table 4.7 (page 224):
type Parameter GL Type Component Conversion ...
------------------------------------------------------------------
... ... ...
UNSIGNED_INT_2_10_10_10_REV uint c = (2^N - 1)f
UNSIGNED_INT_24_8_EXT uint c = (2^N - 1)f (depth only)
Additions to Chapter 4 of the OpenGL 2.0 Specification, as modified by
the EXT_framebuffer_object specification
In section 4.4.2.1 "Renderbuffer Objects", modify the first
paragraph in the definition of RenderbufferStorageEXT to say:
"... must be RGB, RGBA, DEPTH_COMPONENT,
STENCIL_INDEX, DEPTH_STENCIL_EXT, or one of the internal formats
from table 3.16 or table 2.nnn that has a base internal format of
RGB, RGBA, DEPTH_COMPONENT, STENCIL_INDEX, or DEPTH_STENCIL_EXT..."
In section 4.4.4 "Framebuffer Completeness", modify the definition of
"depth-renderable" and "stencil-renderable" to say:
"* An internal format is "depth-renderable" if it is
DEPTH_COMPONENT or one of the formats from table 3.16 whose
base internal format is DEPTH_COMPONENT or DEPTH_STENCIL_EXT.
No other formats are depth-renderable.
* An internal format is "stencil-renderable" if it is
STENCIL_INDEX or DEPTH_STENCIL_EXT, if it is one of the
STENCIL_INDEX formats from table 2.nnn, or if it is one of the
formats from table 3.16 whose base internal format is
DEPTH_STENCIL_EXT. No other formats are stencil-renderable."
In section 4.4.4.2 "Framebuffer Completeness", modify the
duplicate attachment clause of "framebuffer complete" to say:
"* A single image is not attached more than once to the framebuffer
object. The exception is that an image with a DEPTH_STENCIL_EXT
base internal format may be simultaneously attached to both
FRAMEBUFFER_DEPTH_ATTACHMENT and FRAMEBUFFER_STENCIL_ATTACHMENT.
{ FRAMEBUFFER_INCOMPLETE_DUPLICATE_ATTACHMENT_EXT }"
Additions to Chapter 5 of the OpenGL 2.0 Specification (Special
Functions)
None.
Additions to Chapter 6 of the OpenGL 2.0 Specification (State and State
Requests)
Update the third paragraph on page 247, of section 6.1.3 "Enumerated
Queries", to say:
"For texture images with uncompressed internal formats, queries of
value of TEXTURE_RED_SIZE, TEXTURE_GREEN_SIZE, TEXTURE_BLUE_SIZE,
TEXTURE_ALPHA_SIZE, TEXTURE_LUMINANCE_SIZE, TEXTURE_INTENSITY_SIZE,
TEXTURE_DEPTH_SIZE, and TEXTURE_STENCIL_SIZE_EXT return the actual
resolutions of the stored image array components..."
Section 6.1.4, Texture Queries, p. 248, replace the first two
sentences of paragraph two as follows:
"Calling GetTexImage with a color format (one of RED, GREEN,
BLUE, ALPHA, RGB, BGR, RGBA, BGRA, LUMINANCE, or
LUMINANCE_ALPHA) when the internal format of the texture image
is not a color format causes the error INVALID_OPERATION.
Calling GetTexImage with a of DEPTH_COMPONENT when the
base internal format of the texture image is not DEPTH_COMPONENT
or DEPTH_STENCIL_EXT causes the error INVALID_OPERATION.
Calling GetTexImage with a of DEPTH_STENCIL_EXT when
the base internal format of the texture image is not
DEPTH_STENCIL_EXT causes the error INVALID_OPERATION.
GetTexImage obtains component groups from a texture image with
the indicated level-of-detail. If is a color format,
then the components are assigned among R, G, B, and A according
to Table 6.1, starting with the first group in the first row,
and continuing by obtaining groups in order from each row and
proceeding from the first row to the last, and from the first
image to the last for three-dimensional textures. If
is DEPTH_COMPONENT, then each depth component is assigned with
the same ordering of rows and images. If is
DEPTH_STENCIL_EXT, then each depth component and each stencil
index is assigned with the same ordering of rows and images."
Add a row to table 6.17 "Textures (state per texture image)" on page
278:
Get value Type Get Cmd IV Description Sec.
-------------------------------------------------------------------------------------------------------
... ... ... ... ... ...
TEXTURE_STENCIL_SIZE_EXT n x Z+ GetTexLevelParameter 0 texture image's intensity resolution 3.8.3
Update
Dependencies on EXT_framebuffer_object
If EXT_framebuffer_object is not supported, then all discussion of
framebuffer objects and renderbuffer objects should be removed.
GLX Protocol
None.
Errors
The error INVALID_ENUM is generated if DrawPixels or ReadPixels is
called where format is DEPTH_STENCIL_EXT and type is not
UNSIGNED_INT_24_8_EXT.
The error INVALID_OPERATION is generated if DrawPixels or ReadPixels
is called where type is UNSIGNED_INT_24_8_EXT and format is not
DEPTH_STENCIL_EXT.
The error INVALID_OPERATION is generated if DrawPixels or ReadPixels
is called where format is DEPTH_STENCIL_EXT and there is not both a
depth buffer and a stencil buffer.
The error INVALID_OPERATION is generated if CopyPixels is called
where type is DEPTH_STENCIL_EXT and there is not both a depth buffer
and a stencil buffer.
Update the following error in the EXT_framebuffer_object
specification by adding mention of DEPTH_STENCIL_EXT formats:
"The error INVALID_ENUM is generated if RenderbufferStorageEXT is
called with an that is not RGB, RGBA,
DEPTH_COMPONENT, STENCIL_INDEX, DEPTH_STENCIL_EXT, or one of the
internal formats from table 3.16 or table 2.nnn that has a base
internal format of RGB, RGBA, DEPTH_COMPONENT, STENCIL_INDEX, or
DEPTH_STENCIL_EXT."
New State
None.
Usage ExampleS
(1) Attach a DEPTH_STENCIL_EXT texture image to an FBO as both the
depth and stencil buffers.
glGenFramebuffersEXT(1, &fb);
glGenTextures(1, &tex_color);
glGenTextures(1, &tex_depthstencil);
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, fb);
// Setup color texture (mipmap)
glBindTexture(GL_TEXTURE_2D, tex_color);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB8,
512, 512, 0, GL_RGBA, GL_INT, NULL);
glGenerateMipmapEXT(GL_TEXTURE_2D);
glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT,
GL_COLOR_ATTACHMENT0_EXT,
GL_TEXTURE_2D, tex_color, 0);
// Setup depth_stencil texture (not mipmap)
glBindTexture(GL_TEXTURE_2D, tex_depthstencil);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexImage2D(GL_TEXTURE_2D, 0, GL_DEPTH24_STENCIL8_EXT,
512, 512, 0, GL_DEPTH_STENCIL_EXT,
GL_UNSIGNED_INT_24_8_EXT, NULL);
glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT,
GL_DEPTH_ATTACHMENT_EXT,
GL_TEXTURE_2D, tex_depthstencil, 0);
glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT,
GL_STENCIL_ATTACHMENT_EXT,
GL_TEXTURE_2D, tex_depthstencil, 0);
// Check framebuffer completeness at the end of initialization.
loop {
glBindTexture(GL_TEXTURE_2D, 0);
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, fb);
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0);
glBindTexture(GL_TEXTURE_2D, tex_color);
glGenerateMipmapEXT(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D, tex_depthstencil);
}
Issues
01) Depth data has a format of GL_DEPTH_COMPONENT, and stencil data
has a format of STENCIL_INDEX. So shouldn't the enumerant be
called DEPTH_COMPONENT_STENCIL_INDEX_EXT?
RESOLVED: No, this is fairly clumsy.
02) Should we support CopyPixels?
RESOLVED: Yes. Right now copying stencil data means masking off
just the stencil bits, while copying depth data has strange
unintended consequences (fragment operations) and is difficult
to implement. It is easy and useful to add CopyPixels support.
03) Should we support textures?
RESOLVED: Yes. 24-bit depth textures have no good format
without this extension.
04) Should the depth/stencil format support other standard types,
like FLOAT or UNSIGNED_INT?
RESOLVED: No, this extension is designed to be minimalist.
Supporting more types gains little because the new types will
just require data format conversions. Our goal is to match the
native format of the buffer, not add broad new classes of
functionality.
05) Should the 24/8 format be supported for other formats, such as
LUMINANCE_ALPHA? Should we support an 8/24 reversed format as
well?
RESOLVED: No and no, this adds implementation burden and gains
us little, if anything.
06) Should anything be said about performance?
RESOLVED: No, not in the spec. However, common sense should
apply. Apps should probably check that DEPTH_BITS is 24 and
that STENCIL_BITS is 8 before using either the new DrawPixels or
ReadPixels formats. CopyPixels is probably safe regardless of
the size of either buffer. The 24/8 format should probably only
be used with 24-bit depth textures.
07) What happens when the format of a DEPTH_STENCIL_EXT pixel path
operation specifies more components than are present in the
source?
RESOLVED: INVALID_OPERATION is generated.
Operations affected by this issue include ReadPixels and
operations defined in terms of ReadPixels, such as CopyPixels,
CopyTexImage, CopyTexSubImage, and GetTexImage.
For example, if the framebuffer has non-zero DEPTH_BITS but zero
STENCIL_BITS, then ReadPixels of DEPTH_COMPONENT is legal. But
ReadPixels of DEPTH_STENCIL_EXT will generate INVALID_OPERATION.
08) What happens when the format of a DEPTH_STENCIL_EXT pixel path
operation specifies more components than are present in the
destination?
RESOLVED: The extra information is thrown away. No GL error is
generated because the source contains more components than the
destination.
For example, consider a TexSubImage operation where the source
data is DEPTH_STENCIL_EXT but the existing texture format is
DEPTH_COMPONENT.
09) What happens when the format of a DEPTH_STENCIL_EXT pixel path
operation specifies fewer components than are present in the
destination?
RESOLVED: the existing values of the unspecified components are
preserved.
For example, consider a TexSubImage operation where the
is DEPTH_COMPONENT and the existing internalformat is
DEPTH_STENCIL_EXT. The texture image's depth component will be
updated, but the texture's existing stencil component will be
preserved.
10) And, for completeness, what happens when the format of a
DEPTH_STENCIL_EXT pixel path operation specifies fewer
components than are present in the source?
RESOLVED: trivial. Only the specified components are read.
11) How does the texture border color interact with a
DEPTH_STENCIL_EXT texture?
RESOLVED: nothing special needs to be stated here.
There is no stencil component in the border color. Either
you're rendering to it, in which case it's just a buffer, or
texturing from it, in which case stencil is irrelevant. If a
future use case comes up, the second component of
TEXTURE_BORDER_COLOR could be used at the stencil border value,
just as the first component is used as the depth value today.
12) How does automatic mipmap generation deal with the stencil
component of a DEPTH_STENCIL_EXT texture?
RESOLVED: The 2.0 spec doesn't talk about depth textures
specifically. Stencils, which are indexes / counts, are even
harder. We'll leave this undefined.
Also, an application that wants to generate a stencil mipmap can
follow the procedure given in example 5 of the
EXT_framebuffer_object specification.
13) Should GetTexImage permit of DEPTH_STENCIL_EXT?
RESOLVED: Yes.
The GL 2.0 spec disallows GetTexImage of DEPTH_COMPONENT data.
But that seems to be an unintentional spec bug.
ARB_depth_texture permitted it and even addressed the question
as issue 9. Appendix G.4 of the GL 2.0 spec does not mention
this discrepancy.
GetTexImage of DEPTH_STENCIL_EXT format should follow the
resolution for GetTexImage of DEPTH_COMPONENT format.
A future version of the core GL spec will be modified to state
that GetTexImage of DEPTH_COMPONENT data is legal.
14) Does DrawPixels with DEPTH_STENCIL_EXT format behave like
DrawPixels of DEPTH_COMPONENT format, or like DrawPixels of
STENCIL_INDEX format?
RESOLVED: It behaves like DrawPixels of STENCIL_INDEX format.
See sections 3.6.4 and 4.3.1. It is desirable to give similar
treatment to both the depth and the stencil components.
15) If depth/stencil images are mixed such that they violate the
framebuffer completeness rule in section 4.4.4.2, what
FRAMEBUFFER_INCOMPLETE_ enum should be used?
UNRESOLVED: FRAMEBUFFER_INCOMPLETE_ATTACHMENT_EXT and
FRAMEBUFFER_INCOMPLETE_MIXED_DEPTH_STENCIL_EXT are possible
answers.
16) What happens if DEPTH_STENCIL_EXT and STENCIL_ATTACHMENT_EXT
name distinct framebuffer-attachable images, but the format of
one or both is DEPTH_STENCIL_EXT?
RESOLVED: This is permitted. The depth component of the depth
attachment should be updated, the stencil component of the
stencil attachment should be updated, and the other components
are preserved. However, it should be noted that some
implementations might not support such mix-matching, and that
these implementations are free to label such a framebuffer as
FRAMEBUFFER_UNSUPPORTED_EXT.
An earlier drafts of this extension contained the following
language.
In section 4.4.4.2 "Framebuffer Completeness", add a clause
to the definition of "framebuffer complete":
"* If both attachment points FRAMEBUFFER_DEPTH_ATTACHMENT
and FRAMEBUFFER_STENCIL_ATTACHMENT have an attached
image, and if either image's base internal format is
DEPTH_STENCIL_EXT, then the same image must be attached
to both FRAMEBUFFER_DEPTH_ATTACHMENT and
FRAMEBUFFER_STENCIL_ATTACHMENT.
{ FRAMEBUFFER_INCOMPLETE_ATTACHMENT_EXT }"
That clause was removed from section 4.4.4.2 in revision #10
after it was pointed out that, on implementations where such
mix-matching is supported, it need not result in an incomplete
framebuffer.
Revision History
#12 September 26, 2005
- Fix copy/paste error in the example.
#11 September 20, 2005
- Assign enum values.
#10 September 19, 2005
- Remove FRAMEBUFFER_INCOMPLETE_ATTACHMENT_EXT clause and add the
accompanying issue 16 explaining why.
#09 September 19, 2005
- Add issue 15.
- Fix FBO interaction. (depth_stencil can be attached twice)
- Add Usage Examples section and example 1.
- Move issues to the end according to new precedent.
- Add more dependencies, add contributors.
- Fix typos pointed out at ARB meeting.
#08 September 9, 2005
- Resolve issues 13 and 14.
- Add issue 10 for completeness.
- Modify GetTexImage to permit depth and depth/stencil.
- Incorporate feedback from Barthold's review.
#07 August 29, 2005
- Record resolutions for issues 7-12.
- Update the spec body to reflect the issue resolutions.
- Add new issues 13-14.
- Remove interaction with copy_depth_to_color (no resolution needed)
#06 July 15, 2005
- Improve some wording in the issues section.
- Add issue on interaction with NV_copy_depth_to_color.
- Remove interaction with stenci_clear_tag (no resolution needed)
#05 June 20, 2005
- Add (now removed) unresolved issue 12 on interactions with
EXT_stencil_clear_tag.
#04 June 10, 2005
- Add modifications to the EXT_framebuffer_object specification.
#03 May 28, 2005
- Add DEPTH_STENCIL_EXT as a new base internal format,
- Add DEPTH24_STENCIL8_EXT as a new sized internal format.
#02 May 12, 2005
- Update to be written against OpenGL 2.0 specification.
#01 May 12, 2005
- Start with NV_packed_depth_stencil as the basis for
EXT_packed_depth_stencil.
- Rename to EXT.